Imprint lithography (IL) is a technique in which a patterned layer such as a masking layer is formed on a substrate such as a semiconductor substrate or as an optical layer by the deposition of a curable imprintable medium. The curable imprintable medium is subsequently patterned by imprinting the medium with a patterned stamp, after which the curable imprintable medium is solidified e.g. when exposed to light, e.g. UV-light to initiate the curing reaction in the medium. After the curing reaction is completed, the stamp is removed from the medium to leave a patterned layer, e.g. on the semiconductor substrate or on a carrier of such an optical layer.
This technique has recently drawn considerable attention because it can provide a significant cost reduction over traditional lithography process steps. A promising prospect of imprint lithography is that it can be used for forming nanoscale patterns on so-called 2.5D surfaces, i.e. contoured surfaces, which for instance may comprise one or more protrusions, e.g. curved protrusions, emanating from a mainly planar surface. Such techniques may be used to pattern photo-voltaic solar cells, nanowires, VECSEL lasers, medical implants and so on, e.g. by creating nanoscale patterns on optical elements, e.g. lenses or on medical implants, e.g. to stimulate bone or tissue regeneration. To this end, a planar pliable patterned stamp, such as a polysiloxane-based rubber-like stamp, is typically deformed onto the contoured surface such that the stamp pattern is brought into contact with the contoured surface to be patterned. An example of such a stamp is shown in US 2008/0011934 A1.
However, a practical problem remains that it is far from trivial to transfer a pattern from a flexible stamp to all of such a contoured surface. In particular, it is difficult to bring the stamp into contact with a boundary region between a planar section and a (curved) protrusion such that such regions can suffer from incomplete or even absent pattern features. This is because it is far from trivial to deform the pliable stamp to such an extent that it exactly matches the contoured surface. In addition, the high pressures required to force the stamp into these boundary regions reduces the lifetime of the stamp and requires more complicated IL device.